Pullout strength of pedicle screws using cadaveric vertebrae with or without artificial demineralization

Suk-Joong Lee; Jin-Han Lee; Hyun-Joo Lee; Ji Won Oh; Il-Hyung Park

doi:10.1016/j.spinee.2021.04.010

Pullout strength of pedicle screws using cadaveric vertebrae with or without artificial demineralization

Spine J. 2021 Sep;21(9):1580-1586. doi: 10.1016/j.spinee.2021.04.010. Epub 2021 Apr 17.

Authors

Suk-Joong Lee¹, Jin-Han Lee², Hyun-Joo Lee³, Ji Won Oh⁴, Il-Hyung Park⁵

Affiliations

¹ Department of Orthopaedic Surgery, Gyeongsang National University School of Medicine and Gyeongsang National University Changwon Hospital, Changwon, Republic of Korea.
² Department of Orthopaedic Surgery, Kyungpook National University Hospital, 130 Dongduk-ro, Jung-gu, Daegu, Republic of Korea.
³ Department of Orthopaedic Surgery, School of Medicine, Kyungpook National University, 130 Dongduk-ro, Jung-gu, Daegu, Republic of Korea; Department of Orthopaedic Surgery, Kyungpook National University Hospital, 130 Dongduk-ro, Jung-gu, Daegu, Republic of Korea.
⁴ Department of Anatomy, School of Medicine, Kyungpook National University, 130 Dongduk-ro, Jung-gu, Daegu, Republic of Korea; Biomedical Research Institute, Kyungpook National University Hospital, 130 Dongduk-ro, Jung-gu, Daegu, Republic of Korea.
⁵ Department of Orthopaedic Surgery, School of Medicine, Kyungpook National University, 130 Dongduk-ro, Jung-gu, Daegu, Republic of Korea; Department of Orthopaedic Surgery, Kyungpook National University Hospital, 130 Dongduk-ro, Jung-gu, Daegu, Republic of Korea. Electronic address: ihpark@knu.ac.kr.

PMID: 33872804
DOI: 10.1016/j.spinee.2021.04.010

Abstract

Objectives: To evaluate the differences in the pullout strength and displacement of pedicle screws in cadaveric thoracolumbar vertebrae with or without artificial demineralization.

Methods: Five human lumbar and five thoracic vertebrae from one cadaver were divided into two hemivertebrae. The left-side specimens were included in the simulated osteopenic model group and the right-side bones in a control group. In the model group, we immersed each specimen in HCl (1 N) solution for 40 minutes. We measured bone mineral density (BMD) using dual-energy X-ray absorptiometry and quantitative computerized tomography. We inserted polyaxial pedicle screws into the 20 pedicles of the cadaveric lumbar and thoracic spine after measuring the BMD of the 2 hemivertebrae of each specimen. We measured the pullout strength and displacement of the screws before failure in each specimen using an Instron system.

Results: The average pullout strength of the simulated osteopenic model group was 76% that of the control group. In the control and model groups, the pullout strength was 1678.87±358.96 N and 1283.83±341.97 N, respectively, and the displacement was 2.07±0.34 mm and 2.65±0.50 mm, respectively (p<.05). We detected positive correlations between pullout strength and BMD in the control group and observed a negative correlation between displacement and BMD in the model group.

Conclusions: By providing an anatomically symmetric counterpart, the human cadaveric model with or without demineralization can be used as a test bed for pullout tests of the spine. In the simulated osteopenic model group, pullout strength was significantly decreased compared with the untreated control group.

Clinical significance: Decreased bone mineral density may significantly reduce the pullout strength of a pedicle screw, even though the range is osteopenic rather than osoteoporotic.

Keywords: Artificial demineralization; Bone mineral density; Cadaver; Pedicle screw; Pullout strength; Simulated osteopenic model; Spine.

MeSH terms

Biomechanical Phenomena
Bone Density
Cadaver
Humans
Lumbar Vertebrae / surgery
Pedicle Screws*
Thoracic Vertebrae / surgery